Composite wood products are made from elements or particles of wood, commonly called furnish, which are consolidated and bonded together with adhesive resin(s). It should be understood that, in the present application, the terms “element”, “particle” and “furnish” may be used interchangeably and may refer to any type of element from which a composite wood product may be manufactured. It should further be understood that wood composites, as defined in this specification, refer to those products which maintain the main properties of wood. Wood elements may include, for example, wood flour, fiber, fiber bundles, flakes, chips, wafers, strands, veneers, or combinations of the like. Different grades and/or types of composite wood products can be manufactured depending on, for example, the wood species, size of the wood elements, and processing conditions. The elements are dried to the moisture content level required by the process. Then adhesive, biocides, and other types of additives such as, for example, waxes, are applied to the furnish. This process may occur at one of many stages of manufacture, but commonly would occur during a process referred to as blending. Usually the blended furnish is then formed into a mat, which is then consolidated under heat and pressure to form the final composite wood product.
Certain biocides can be applied to the furnish to impart decay and/or insect resistance in the final product. Biocides typically used in industrial applications include, for example, inorganic compounds, such as zinc borate, sodium borate, or copper-containing salts. Many types of inorganic compounds may be used as single preservatives, or may be used in combination with other compounds as co-biocides to treat wood fragments prior to formation of a composite wood product.
Controlling biocide additive content may be critical to ensure proper concentration and distribution of active ingredients in the product. Uniform biocide distribution across the product enables economical and proper product protection against insects and fungi, including decay. Non-uniform concentration or distribution may lead to partial damage of the product by fungi or insects. Uniformity of biocide distribution depends on the method of application. During application, a variety of accidental factors may appear which may result in non-uniform distribution of biocides or application of biocides in quantities outside the target range. Examples of some problems include clogging of a spray nozzle with dust, contamination in biocide dispersion, a faulty dispensing system, etc. In a production setting, such as a commercial setting, it is difficult to quantify uniformity of treatment simply from the appearance of the blended wood furnish or in the final composite wood product. As a result, special analytical methods must be applied to the product to identify active ingredient concentration and distribution.
It has been found that wood preservatives containing certain elements, for example, chlorine, zinc and/or copper and/or chromium and/or arsenic, could be analyzed relatively quickly without special sample preparation via x-ray fluorescence spectroscopy (“XRF”). This was particularly the case if such elements were introduced into the wood product in sufficient concentration (above 1000 ppm, but in some cases as low as 30 ppm). XRF analysis allows for the non-destructive analysis of a wide range of elements, typically those heavier than Fluorine (F). The basic principle behind XRF spectroscopy is the use of an energy source to excite an inner shell electron of an atom. Energy is applied from a source, for example an appropriate radioisotope, under which the atom will emit an x-ray photon (fluoresce). If the applied energy is of sufficient strength, an electron will be ejected from an inner ring. This electron will be replaced by an electron from an outer ring in order to stabilize the atom. The movement of an electron to stabilize the atom will emit an x-ray photon, which is counted by the detector.
It was also found that preservatives containing organic compounds such as deltamethrin, chlorpyrifos or isothiazolone require a target application level onto a wood product often as low as 10 ppm to 2000 ppm. However, elements sensitive to XRF analysis are not present or present in less than sufficient concentrations to enable quick and accurate analysis of these products. Products treated with organic biocides require complex sample preparation and sophisticated analytical methods, such as, for example, High Performance Liquid Chromatography (HPLC), Gas Chromatography (GC), or Neutron Activation Analysis (NAA). Even in isolated cases where sample preparation is not a major issue, these methods require specialized and expensive equipment, as well as trained personnel. Neither is readily available or practical in a composite wood manufacturing facility. The delay associated with such sophisticated analytical methods can be a major problem because it potentially allows faulty product to be manufactured without timely detection of defects. A need, therefore, exists for a method of determining a concentration and distribution of a biocide within a composite wood product which is more convenient than known methods.